If you look up at your roof and see black stains covering the shingles, you may immediately think your home is now home to a deadly fungus. Luckily for everyone in the area, what you’re seeing probably isn’t black mold, but rather a type of algae.
Algae growth on the roof is common throughout the eastern United States and along the western coastbasically anywhere with relatively high humidity. If your roof is covered in black streaks, you’re likely wondering what exactly it is, how it affects your roof, and what you can do about it.
What is Algae?
When you think of algae, you probably think about underwater plants that blanket the bottom of the neighborhood pond. How did that get onto your roof? “Algae” is actually a broad term used to describe many different varieties of organisms that rely on photosynthesis for nutrition. All algae lacks connective tissues that transport nutrients between cells, meaning each cell must absorb its own nutrients.
This nonvascular system sets algae apart from plants and is the reason why most algae thrives in underwater environments. The algae on your roof is Gloeocapsa magma, also known as blue-green algae. It’s a single-celled organism with a unique ability to build a protective sheath around itself to shield it from UV radiation.
Because the algae that grows on your roof is a colony, rather than a single organism, it doesn’t need to be submersed in water to thrive. And because of the protective covering that allows it live where other algae cannot-in direct sunlight-blue-green algae finds a perfect home on your roof. And once it settles, it grows quickly and spreads spores through the air, possibly onto your neighbor’s roofs.
How Does Algae Affect the Roof?
For the most part, blue-green algae doesn’t pose much of a risk to the structural stability of your roof. Its main detriment is that it looks slimy and dirty, and can make your home less appealing to potential buyers. Even if you aren’t planning on selling the house, if you take pride in your property, you probably don’t want a grimy black roof ruining the aesthetic.
Also, if you have an energy-saving cool roof that reflects sunlight and keeps the temperature of your home low, you probably don’t want a colony of algae blocking the reflective panels and ruining your investment.
How Do You Clean It Off?
If you’re tired of the unsightly black smears streaking across your roof, you can take steps to clear it off. Cleaning algae off your roof is a fairly simple process, but if you don’t feel comfortable doing it on your own, don’t hesitate to call in a professional.
All you need for the cleaning is a low pressure water sprayer and a half-and-half solution of bleach and water. Spray the solution onto the roof, let it sit for a quarter of an hour, then rinse it off with pure water. Be careful not to let the solution dry onto the roof, as it will be harder to rinse off. Performing the cleaning on a cloudy day will help prevent fast dry times.
Keep in mind how bleach affects the rest of your property. Spray down any bushes or plants near your house with pure water, then cover them with some kind of tarp. Protect yourself as well with gloves and safety glasses.
The initial cleaning won’t immediately wipe away all the algae, but don’t keep spraying or scrubbing if you don’t see the algae loosen immediately. This will only damage your roof. Just have patience; the bleach slowly kills the algae, which then falls off or washes away in the rain.
What if the Algae Returns?
Now that blue-green algae spores are present in the environment, it’s possible that a colony will start growing on your roof again. To prevent that from happening, there are a couple of steps you can take.
One option is to install a metal sheet along the sides and top of your roof. Copper works best, although it can be expensive. Zinc is another successful option. During rainfall, small metal particles will wash down the roof. These particles are toxic to algae, so the colony will die before it really has a chance to take hold.
You can also trim away tree branches that shade the roof, as full sunlight is detrimental to blue-green algae that doesn’t have its UV-protective covering yet. Make sure you remove excess debris and clean the gutters to limit the amount of standing moisture on the roof.
If your roof is older and you’re already thinking about replacing it, consider looking into algae-proof shingles. These shingles contain tiny copper particles that kill the algae spores on contact, so the organisms never have a chance to start growing in the first place. A metal roof, especially one made of copper, will discourage algae growth and give your home a fresh appearance.
Talk to American Building & Roofing Inc about your options for replacing your roof, both to keep away algae and to offer stronger protection for your home.